The present invention relates to structures for supporting palletys in general, and to rack systems which receive plastic pallets in particular.
The second half of the 20th century has seen the widespread use of pallets for the effective and economical storage and transport of goods and commodities of all kinds. Palletized material handling means that goods are handled not as distinct custom loads, but as repeatable elements in a streamlined flow. The tremendous economic advantage to handling material on pallets, as opposed to specialized containers, has supported an enormous investment throughout the world in standardized material handling equipment including hand trucks, forklift vehicles, and rack storage systems. For decades, the wooden pallet assembled from hardwood planks and steel nails has been the world standard. Much of the support infrastructure has been configured to accommodate the attributes of a hardwood pallet. Pallet handling equipment and pallet supports are tailored to the rigidity, maximum deflection, and strength of a wooden pallet.
Nevertheless, despite the widespread acceptance of wooden pallets there is also a growing acknowledgment of the inadequacies of wood in today's demanding pallet environment. Pallets made of plastic are splinter and rust free, resistant to rot, uniform, nestable, easily adapted to custom cargoes, and have a greatly extended useful life when compared to wooden pallets. Even with these many benefits, there are certain attributes of plastic which cannot be overlooked. First, if the plastic is to be resilient enough to withstand the rough treatment of commercial transportation, it will be of lower strength and rigidity than wood. Second, plastic by weight is usually more costly than wood.
By the use of reinforcements and thoughtful engineering, a plastic pallet can be designed to equal the performance of a wooden pallet in terms of maximum deflection, load carrying capability, and length of unsupported span. However, a pallet requiring significant additional material comes at a measurable increase in cost. When the vast scale of local, national, and international material flows is taken into account, with their large inventories of pallets, the cost of conversion can be daunting.
A pallet is subjected to a variety of different loading conditions at different stages in the transportation system. At rest, all the pallet legs are disposed on a planar floor or an underlying load. In transport, the pallet deck supports the loads on the tines of a lift truck. A particularly demanding loading condition is rack support in which the outer legs of the pallet carry the full load. Wooden timbers perform very well when crossing an open span. To match this performance a plastic pallet will typically require reinforcement with metal or other material, with a significant increase in pallet cost.
Numerous warehouses throughout the country are outfitted with pallet supporting rack systems having thousands of positions to receive loaded pallets. These rack systems are generally configured to receive wooden pallets, and represent an enormous investment in infrastructure. These rack systems typically have front and rear beams which support the pallet in a clear span. Metal mesh decks are available which extend between the rack front and rear beams and which support smaller or less stiff loads. However, these mesh decks are usually uniform arrays of rods or wires and not particularly adapted to minimizing deflection. Moreover, the plastic pallet can be marred or deformed if too great a load is carried on a single wire. Rather than utilize costly reinforced plastic pallets which can be employed with historic rack systems, low cost pallets could be used if a rack support system were available which did not impose such challenging demands on the pallet. An additional benefit is the purchaser of the rack deck maintains control over the investment, and it will far outlast the life of any particular pallet. If a deck could be supplied which permitted the use of lower cost pallets, and which could be acquired for about the cost differential between a plastic pallet of rigidity similar to wood, and one which is not, the conversion to widespread use of the advantageous plastic pallets would be greatly facilitated.
What is needed is an economical deck which can be retrofitted to conventional rack systems to support conventional plastic pallets to provide a cost-effective plastic pallet storage system.